1. Field of the Invention
The present invention relates to nuclear magnetic resonance (NMR) apparatuses and, more particularly, to a low magnetic field/very low magnetic field NMR apparatus.
2. Description of the Related Art
Nuclear magnetic resonance (hereinafter referred to as “NMR”) is a phenomenon involved with precession of the magnetic spin of an atomic nucleus arising from resonance of the magnetic spin of the nucleus under a strong magnetic field when the magnetic field is applied to the atomic nucleus. Magnetic resonance imaging (hereinafter referred to as “MRI”) is a non-invasive technique of imaging the inner part of a target object by detecting electromagnetic waves generated during the precession using the NMR. The MRI is widely used as a medical diagnostics tool to image the inner part of human body.
Sensitivity of an MRI image is in proportion to a magnetization (polarization) strength and a resonant frequency of a nucleus. In general, a very strong main magnetic field using a superconducting magnet is applied to a target material to improve the sensitivity of the MRI image. Thus, the magnetization strength and the resonant frequency of the nucleus increase.
Relaxation time of an NMR signal is in inverse proportion to uniformity of the main magnetic field. Thus, strength and uniformity of the main magnetic field are important.
High cost is required to product a superconducting magnet generating a uniform magnetic field having a strength of several Tesla (T). In addition, the operation of the superconducting magnet uses liquid helium that is an expensive refrigerant. Thus, maintenance cost of an MRI system using the superconducting magnet increases.
A low/very low magnetic field NMR and MRI (hereinafter integrally referred to as “low magnetic field MRI”) is a new conceptual MRI apparatus operating at a magnetic filed having a strength of several micro Tesla to hundreds of micro Tesla. In a conventional MRI apparatus, a magnetization strength and a resonant frequency of a nucleus increase to improve sensitivity of an image. However, in the low magnetic field MRI apparatus, a main magnetic field generated from a magnet of a conventional MRI apparatus is split into a prepolarization magnetic field and a measurement magnetic field. The measurement magnetic field may have a strength of about several micro Tesla (uT) to about tens of uT.